Don't fail if branch has no pipeline definition

[pat-s]

Component

server, web-ui

Describe the bug

In a repo where builds are only desired for a specific branch (excluding the default branch), the following happens:

• On a push to a custom branch which has a valid pipeline definition, everything works
• On a push to any other of the repo the webhook is also triggered but the build will immediately fail due to a missing pipeline config

The use case I have here is that I maintain a fork. I build some stuff in a custom branch but always keep main/master in sync with upstream.
Hence, only the custom branch has a pipeline definition and whenever the main branch is synced with upstream, the above error occurs.

I think it would be good if WP first checks for any existence of a valid WP YAML file and if none is found, just does nothing - instead of throwing an error?

System Info

next-8629a418f8

Additional context

No response

Validations

• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Checked that the bug isn't fixed in the next version already [https://woodpecker-ci.org/faq#which-version-of-woodpecker-should-i-use]
• Check that this is a concrete bug. For Q&A join our Discord Chat Server or the Matrix room.

[anbraten]

linking #2313

[qwerty287]

Duplicate #2312